This invention generally pertains to measuring devices. More specifically, the present invention relates to a device for measuring electrical current and, optionally, several other parameters.
The invention is particularly applicable to a current density measuring device which is utilized in an electrodeposition system in which a metallic body is positioned in an electrolyte. The primary measurement environment for the apparatus is an automotive electrocoating facility maintained either at an automobile plant or in a laboratory. However, it should be appreciated by those skilled in the art, that the invention has broader applications and may also be adapted for use in other environments where a measurement of current and, optionally, other parameters is required.
Electrodeposition of aqueous non-conductive polymer coatings onto a metallic substrate has risen to industrial prominence in recent years. This type of deposition process is generally considered to be a type of electrophoresis. The process has many advantages including relative uniformity and completeness of coating, even on intricate shapes. Virtually any electrically conductive substrate can be coated, however the process has been primarily employed to prime ferrous metal substrates.
The electrodeposition coating process (E-Coat) has become increasingly important in the coatings industry, because by comparison with non-electrophoretic coating means, electrodeposition offers higher paint utilization, outstanding corrosion protection, and low environmental contamination. Initially, the work piece being coated served as the anode in the electrodeposition process. This was familiarly referred to as anionic electrodeposition. However, in the early 1970's, cationic electrodeposition, in which the metallic part to be coated serves as the cathode, was introduced commercially. Since that time, cationic electrodeposition has steadily gained in popularity and is today by far the most prevalent method of electrodeposition. Currently, more than 80% of all motor vehicles produced around the world are given a base coat or a primer coat by cationic electrodeposition.
The process involves immersing the car body or car parts in a conductive electrolyte bath in a tank. The E-Coat bath is a water thin electrolytic resin mixture that is kept in the tank under constant turbulent agitation. The car body becomes a cathode and several anodes are attached to tank walls to act as the other electrode in the circuit. A direct current voltage between approximately 200 to 400 volts is applied between the cathode and the tank anodes. When proper conditions occur at the metal surface, i.e. correct pH, minimum current density, etc., the resin precipitates onto the metal. The resin forms a film which, after curing, can be on the order of between 1 to 2 mils (0.0254 to 0.0508 millimeters) in thickness.
Ideally, a uniform coating thickness is desired on all body surfaces. Problems arise when non-uniform deposition occurs causing widely varying thicknesses of resin coating on different parts of the body. This can cause the car body to be rejected and scrapped, at a tremendous expense to the vehicle manufacturer. Even if the body is used, uneven coatings can lead to an early corrosion of the portion of the body which was not coated with a sufficiently thick layer of the resin.
Since electrocoating is a current driven process, measurement of the current density on different parts of a car body would provide data on and an insight into how the process could be optimized to obtain a more uniform coating layer on the car body. Collected data would aid in solving problems occurring in electrocoating systems presently installed as well as aid in the design of new electrocoating facilities.
At the moment, no suitable current measuring device exists for this type of environment. Standard current measuring devices are not sensitive enough to measure the current density in an E-Coat bath with precision. Additionally, no standard current measuring devices are available which can be used in the harsh and corrosive E-Coat bath environment. It would be advantageous to provide such a current measuring device. It would also be advantageous to provide an apparatus which is capable of measuring several different parameters in an environment having a metallic body positioned in an electrolytic bath.
Accordingly, it has been considered desirable to develop a new and improved current measuring device, as well as an apparatus which can be used for measuring current density and other parameters, which would overcome the foregoing difficulties and others and meet the abovestated needs while providing better and more advantageous overall results.